Unfortunately, all teachers use different spelling words for their classroom. Teachers from the same school don't even use the same spelling list. They all have their own spelling words. In fact, kids from the same class may have an entirely different spelling words. In my son's second grade class, each kids' spelling list for the week depends on the word(s) he or she missed on the spelling test on Friday. So, in theory, each child can have a different spelling word/list.
No worries, I am sure your son can make up for the homework that he missed today.